Clean effective punching is the name of the game when boxing and it's the punch you don't see coming that gets you. The left hook is a punch thrown tight on the inside that opponents don't see coming because of the distance and angle it comes from. The right uppercut (slightly more powerful than the left uppercut) is another punch effective for knockouts because it's thrown tight and on the inside. They NEVER see this one coming too unless they are looking down.
Embrace the pain...train hard bro...TRAIN!